Thermosetting powdery coating composition

ABSTRACT

The thermosetting powdery coating composition of the invention comprises (A) from 40 to 98 parts by weight of a fluorinecontaining copolymer, which is a copolymer of a fluoroolefin and a comonomer having a crosslinkable reactive group, e.g., hydroxy, carbonyl, amino and glycidyl groups, containing at least 10% by weight of fluorine and having an intrinsic viscosity of 0.05-2 dl/g (30° C., tetrahydrofuran) and a glass transition temperature of 30°-120° C. and (B) from 60 to 2 parts by weight of a curing agent capable of forming crosslinks by reacting with the crosslinkable reactive groups in (A). The powdery coating composition of the invention is excellent in the dispersibility of pigments and efficiency in the coating works therewith and capable of giving a coating film having improved adhesion to the substrate surface, surface luster, impact resistance and insusceptibility to stain.

This application is a continuation of application Ser. No. 07/224,054,filed Jul. 25, 1988 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a thermosetting powdery coatingcomposition having excellent dispersibility of pigments and workabilityin coating works and capable of forming a coating film having excellentsurface luster, insusceptibility to stains, impact resistance,weatherability and the like.

As is known, the techniques of powder coating are widely practiced inrecent years for coating of metal-made bodies in general by virtue ofthe advantages in respect of material saving and energy saving as wellas absence of problems due to environmental pollution. In particular,the techniques of powder coating are useful for coating of varioussubstrate bodies of which high weatherability of the coating films isessential such as transportation and living structures, e.g., bridges,parapets, gates, fences, sidings of houses and the like, bodies andparts of automobiles, electric applicances and so on.

Powdery coating compositions used for powder coating are classified intothermoplastic and thermosetting powder coating composition depending onthe type of the polymeric resin as the vehicles. For example, JapanesePatent Kokai 61181567, 61-181571 and 61-181572 disclose a thermoplasticpowder coating composition of which the vehicle resin is a thermoplasticfluorocarbon resin such as a copolymer of ethylene andtetrafluoroethylene.

Several kinds of thermosetting powdery coating compositions used forpowder coating are also known including polyester resinbased powderycoating compositions using a blocked isocyanate compound, triglycidylisocyanurate and the like as the curing agent and powder coatingcompositions based on acrylic resins having glycidyl groups and using adibasic acid as the curing agent (see, for example, "Funtai to Kogyo",February, 1984 issue, pages 33 to 42).

Though excellent in the weatherability of the coating films, the firstmentioned thermoplastic fluorocarbon resin-based powdery coatingcompositions have several disadvantages that, in addition to the poordispersibility of pigments, surface luster of the coating films andadhesion of the coating film to the substrate surface, the coatingcomposition must be heated in the coating works to a temperature higherthan the high melting point of the fluorocarbon resin consequently withpoor workability and consumption of a large quantity of thermal energy.

The thermosetting powder coating compositions such as the abovementioned polyester resin-based and acrylic resin-based ones, on theother hand, are defective due to the relatively low weatherability ofthe coating films although they are free from the above mentionedproblems in the thermoplastic fluorocarbon resin-based powdery coatingcompositions.

SUMMARY OF THE INVENTION

The present invention accordingly has an object to provide a novel andimproved thermosetting powdery coating composition having excellentdispersibility of pigments and workability in the coating works andcapable of forming a coating film having excellent adhesion to thesubstrate surface, surface luster, insusceptibility to stain and impactresistance as well as high weatherability not inferior to thermoplasticfluorocarbon resin-based powdery coating compositions.

The thermosetting powdery coating composition of the present inventiondeveloped as a result of the extensive investigations undertaken withthe above mentioned object comprises (A) a specific reactivefluorine-containing copolymer and (B) a curing agent for the component(A).

In particular, the thermosetting powdery coating composition of theinvention comprises, in admixture: (A) from 40 to 98 parts by weight ofa fluorine-containing copolymer comprising a monomeric moiety derivedfrom a fluoroolefin compound and having crosslinkable reactive groups,of which the content of fluorine is at least 10% by weight, theintrinsic viscosity determined at 30° C. in tetrahydrofuran is in therange from 0.05 to 2 dl/g and the glass transition temperature is in therange from 30° to 120° C.; and (B) from 60 to 2 parts by weight of acuring agent capable of forming crosslinks by reacting with thecrosslinkable reactive groups in the fluorine-containing copolymer asthe component (A).

As to the density of the crosslinkable reactive groups in the polymericmolecules of the fluorine-containing copolymer as the component (A), itis particularly preferable that the average molecule weight of thepolymeric molecular chains is in the range from 250 to 25,000 per one ofthe crosslinkable reactive groups.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is described above, the base ingredient in the inventivethermosetting powdery coating composition is a fluorine-containingcopolymer comprising a monomeric moiety derived from a fluoroolefincompound and having crosslinkable reactive groups.

The fluoroolefin compound as one of the constituents of thefluorine-containing copolymer as the component (A) of the inventivecomposition is exemplified by tetrafluoroethylene,chlorotrifluoroethylene, trifluoroethylene, vinylidene fluoride,hexafluoropropylene, pentafluoropropylene and the like and appropriatelyselected depending on the properties required of the coating film andthe comonomer to be copolymerized therewith or the curing agent as thecomponent (B) combined with the fluorine-containing copolymer. It is ofcourse optional according to need that two kinds or more of thefluoroolefin compounds are used in combination.

The above mentioned crosslinkable reactive group in thefluorine-containing copolymer is exemplified by hydroxy group, carboxylgroup, amido group, amino group, mercapto group, glycidyl group, activehalogens, e.g., bromine and iodine, isocyanate group and the like. It isoptional that two kinds or more of these reactive groups are containedin the same fluorine-containing copolymer.

The crosslinkable reactive groups can be introduced into thefluorine-containing copolymer by several methods including a method inwhich a monomer having the crosslinkable reactive group is copolymerizedwith the fluoroolefin compound, a method in which a specific precursorcopolymer is subjected to partial decomposition to form thecrosslinkable reactive groups, a method in which a precursor copolymerhaving functional groups is reacted with a compound having acrosslinkable reactive group, and so on.

The above mentioned method of copolymerization can be performed, forexample, by copolymerizing a fluoroolefin compound with a monomericcompound having polymerizable ethylenic unsaturation and having, as apreferable crosslinkable reactive group, a hydroxy group or a groupconvertible into a hydroxy group. Examples of such a monomeric compoundhaving a hydroxy group or a group convertible into a hydroxy groupinclude hydroxyalkyl vinyl ethers, e.g., hydroxyethyl vinyl ether,hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxy isobutylvinyl ether, hydroxycyclohexyl vinyl ether and the like, vinylhydroxysubstituted carboxylates, e.g., vinyl hydroxyacetate, vinylhydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinylhydroxy isobutyrate, vinyl hydroxycyclohexane carboxylate and the like,hydroxyalkyl allyl ethers, e.g., hydroxyethyl allyl ether, hydroxypropylallyl ether, hydroxybutyl allyl ether, hydroxy isobutyl allyl ether,hydroxycyclohexyl allyl ether and the like, hydroxyalkyl allyl esters,e.g., allyl hydroxyacetate, allyl hydroxypropionate, allylhydroxybutyrate, allyl hydroxy isobutyrate, allyl hydroxycyclohexanecarboxylate and the like, and hydroxyalkyl acrylates and methacrylates,e.g., 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethylmethacrylate, hydroxypropyl methacrylate and the like, as well asderivatives thereof by substitution of fluorine atoms for a part ofhydrogen atoms. It is optional that two kinds or more of these monomersare used in combination according to need. In view of thecopolymerizability with the fluoroolefin compound, it is preferable touse the vinyl monomers or allyl monomers among the above namedcompounds.

The monomeric compounds having a carboxyl group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by acrylic acid, methacrylic acid, carboxyalkyl allyl ethersand the like.

The monomeric compounds having a glycidyl group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by glycidyl acrylate, glycidyl methacrylate, glycidyl vinylether, glycidyl allyl ether and the like.

The monomeric compounds having an amino group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by aminoalkyl vinyl ethers, aminoalkyl allyl ethers and thelike.

The monomeric compounds having an amido group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by acrylamide, methacrylamide, N-methylol acrylamide and thelike.

The monomeric compounds having an nitrile group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by acrylonitrile, methacrylonitrile and the like.

The monomeric compounds having an isocyanate group as the crosslinkablereactive group and copolymerizable with the fluoroolefin compound areexemplified by vinyl isocyanate, isocyanatoethyl acrylate and the like.

The monomeric compounds having an active halogen atom as thecrosslinkable reactive group and copolymerizable with the fluoroolefincompound are exemplified by vinyl chloride, vinylidene chloride and thelike.

The method for the preparation of the copolymer as the component (A) bythe partial decomposition of a precursor copolymer is performed, forexample, by first copolymerizing the fluoroolefin compound with amonomer having an ester group susceptible to hydrolysis aftercopolymerization and then hydrolyzing the copolymer to produce carboxylgroups in the copolymer.

Alternatively, the ester groups introduced into the polymeric moleculescan be utilized directly as the crosslinkable reactive groups in thecuring reaction by an ester exchange reaction without being hydrolyzedbeforehand into carboxyl groups.

The method for the preparation of the copolymer as the component (A) bythe polymer reaction of a precursor copolymer with a compound capable ofgiving a crosslinkable reactive group is performed, for example, by areaction of a hydroxycontaining copolymer with an anhydride of a dibasiccarboxylic acid such as succinic anhydride and the like to introducecarboxylic groups into the molecular structure of the copolymer.

It is optional or sometimes preferable that the fluorine-containingcopolymer as the component (A) is prepared by the copolymerization of afluoroolefin compound, a comonomer for introducing crosslinkablereactive groups and, further, one or more of other comonomerscopolymerizable with the former two comonomers with an object todecrease the melting point or glass transition temperature of thefluorine-containing copolymer and to further improve the workability inthe coating works by using the inventive coating composition or toimpart the coating films formed from the inventive coating compositionwith desirable properties such as appropriate hardness, flexibility,surface luster and the like.

Such a third comonomer should have an active ethylenically unsaturatedlinkage copolymerizable with the fluoroolefin compound and should haveno adverse influences on the weatherability of the coating films formedfrom the inventive coating composition. Examples of a monomeric compoundsuitable as the third comonomer include alkyl vinyl ethers, e.g., ethylvinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinylether, cyclohexyl vinyl ether and the like, vinyl carboxylates, e.g.,vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate,vinyl valerate, vinyl cyclohexane carboxylate and the like, alkyl allylethers, e.g., ethyl allyl ether, propyl allyl ether, butyl allyl ether,isobutyl allyl ether, cyclohexyl allyl ether and the like, allylcarboxylates, e.g., allyl acetate, allyl propionate, allyl butyrate,allyl isobutyrate, allyl cyclohexylate and the like, alkenes, e.g.,ethylene, propylene, butylene, isobutylene and the like, acrylic andmethacrylic acids and esters thereof, e.g., ethyl acrylate, propylacrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate,ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutylmethacrylate, 2-ethylhexyl methacrylate and the like, and so on as wellas derivatives thereof by substitution of fluorine atoms for a part ofthe hydrogen atoms therein, of which vinyl, allyl and alkene compoundsare preferred in view of the copolymerizability with the fluoroolefincompound. These monomeric compounds can be used either singly or as acombination of two kinds or more according to need. When the thirdcomonomer is a vinyl or allyl carboxylate or a vinyl or allyl alkylether, it is preferable that the carboxyl group in the ester or thealkyl group in the ether has 2 to 10 carbon atoms and the structurethereof is straightly linear, branched or alicyclic.

It is important that the fluorine-containing copolymer as the component(A) in the inventive thermosetting powdery coating composition containsat least 10% by weight of fluorine. The fluorine content of thecopolymer is usually related to the molar fraction of the monomericmoiety in the copolymer derived from the fluoroolefin compound as one ofthe comonomers. It is a possible way, however, that the fluorine contentof the copolymer is increased or decreased by a polymer reaction of acopolymer prepared by the copolymerization of the comonomers in asuitable proportion.

When the fluorine content of the fluorine-containing copolymer as thecomponent (A) is lower than 10% by weight, no sufficiently highweatherability can be imparted to the coating film formed from thecoating composition. It is particularly preferable that the fluorinecontent of the fluorine-containing copolymer as the component (A) is inthe range from 15 to 72% by weight from the standpoint of obtaining agood balance between the weatherability of the coating films and theworkability in the coating works with the inventive powdery coatingcomposition.

In addition to the limitation that the fluorine content thereof is atleast 10% by weight, it is preferable that the fluorine-containingcopolymer as the component (A) in the inventive composition is composedof the monomeric units of which from 30 to 70% by moles are the unitsderived from the fluoroolefin compound. A remarkable improvement can beobtained in the weatherability of the coating film when thefluorine-containing copolymer contains 30% by moles or more of thefluoroolefin units. The upper limit of 70% by moles of the fluoroolefinunits is given in consideration of the advantages obtained thereby thatthe fluorine-containing copolymer is predominantly amorphous ornon-crystalline so that the coating film formed from the coatingcomposition may have a uniform and smooth surface and exhibit goodadhesion to the substrate surface and, moreover, the baking treatment ofthe coating films can be performed at a reasonable temperature notunduly high.

The fluorine-containing copolymer as the component (A) in the inventivethermosetting powdery coating composition has crosslinkable reactivegroups which pertain to the reaction with the curing agent as thecomponent (B) to give a tenacious coating film exhibiting good adhesionto the substrate surface. In this regard, the density of thecrosslinkable reactive groups in the fluorine-containing copolymer is animportant factor. For example, the average molecular weight of thecopolymeric molecules per one of the crosslinkable reactive groups ispreferably in the range from 250 to 25,000. When the density of thecrosslinkable reactive groups is too small, the crosslinking density inthe coating film is too low so that the coating film has poor propertiessuch as decreased solvent resistance. When the density of thecrosslinkable reactive groups is too high, on the other hand, thecrosslinking density in the coating film is too high to cause a decreasein the flexibility of the coating films.

The above mentioned average molecular weight of the molecular chain perone of the crosslinkable reactive groups of the fluorine-containingcopolymer is a value given by: ##EQU1## More particularly, the averagemolecular weight implied above is given by:

    [56.1/(value of crosslinkable reactive groups)]×10.sup.3,

in which the numerical figure 56.1 corresponds to the molecular weightof potassium hydroxide KOH and the value of crosslinkable reactivegroups is the hydroxy value, acid value, epoxy equivalent or the likegiven in mg KOH/g as determined by the methods of infrared absorptionspectrophotometric analysis, NMR spectrometric analysis, chemicaltitrimetric analysis and the like.

When the crosslinkable reactive group is an epoxy group, the epoxyequivalent can be used as the value of the crosslinkable reactivegroups.

When the crosslinkable reactive groups of the fluorine-containingcopolymer as the component (A) are hydroxy groups, the copolymer shouldpreferably have a hydroxyl value in the range from 1 to 200 mg KOH/g or,more preferably, from 20 to 140 mg KOH/g. When the hydroxyl value is toosmall, the coating film may have poor properties due to the deficiencyin the crosslinking density. When the hydroxyl value is too large, onthe other hand, the flexibility of the coating films may be somewhatdecreased due to the excessively high crosslinking density.

It is also essential that the fluorine-containing copolymer as thecomponent (A) in the inventive coating composition has an intrinsicviscosity as determined at 30° C. in tetrahydrofuran in the range from0.05 to 2 dl/g. When the intrinsic viscosity of the copolymer is toolow, the copolymer cannot be a solid capable of being divided into fineparticles so that the copolymer cannot be used as a constituent of thepowdery coating composition. When the intrinsic viscosity of thecopolymer is too high, on the other hand, the powdery coatingcomposition may have decreased spreadability due to the increase in thesoftening point of the copolymer not to give a uniform coating film.

It is also important that the fluorine-containing copolymer has a glasstransition temperature in the range from 30° to 120° C. or, preferably,from 35° to 100° C. When the glass transition temperature of thecopolymer is too low, the copolymer cannot be a solid capable of beingfinely divided into fine particles so that the copolymer cannot be usedas a constituent of the powdery coating composition. When the glasstransition temperature of the copolymer is too high, on the other hand,the powdery coating composition may have decreased spreadability due tothe increase in the softening point of the copolymer not to give auniform coating film.

It is not preferable that the fluorine-containing copolymer used as thecopolymer (A) has a high crystallinity because the baking treatment of acoating film by use of such a copolymer must be performed at anincreased temperature. A fluorine-containing copolymer havingcrystallinity, however, can be used as the component (A) when themelting point thereof does not exceed 200° C.

The fluorine-containing copolymer used as the component (A) can beprepared by several known methods. For example, the comonomers inadmixture with addition of a polymerization initiator are copolymerizedin the presence or absence of a catalyst. The copolymerization reactioncan be performed in any procedure of solution polymerization, emulsionpolymerization and suspension polymerization.

Since the fluorine-containing copolymer is used as the component (A) inthe inventive coating composition in a powdery form, it is importantthat the copolymerization reaction is performed in such an appropriatemanner depending on the respective type of the polymerization reactionthat the copolymer can be obtained in a powdery form of a desiredfineness.

When the fluorine-containing copolymer is prepared by a process ofemulsion polymerization or suspension polymerization, the polymerizationmedium is removed from the polymerizate mixture by evaporation at atemperature of 50° to 100° C. under a reduced pressure of 10 mmHg orbelow and the dried polymerizate is pulverized by using a suitablepulverizing machine such as Willie type, vibration mill type and hammermill type ones. When the fluorine-containing copolymer is prepared by aprocess of solution polymerization, the solvent of the polymerizatesolution is evaporated to leave the copolymer in a dry form or thepolymerizate solution is poured into another solvent having nodissolving power of the copolymer so as to precipitate the copolymer inthe mixture which is collected by filtration and dried followed bypulverization.

The fluorine-containing copolymer used as the component (A) in the formof a finely divided powdery form should be as completely dry aspossible. It is desirable in this regard that the residual content ofthe solvent or the polymerization medium contained therein, which can bedetermined as a weight loss by heating, does not exceed 5% by weight.When the powdery fluorine-containing copolymer contains an excessivelylarge amount of the residual solvent or polymerization medium, severaldisadvantages are caused thereby that the storage stability of thepowdery coating composition is decreased and that foams, blisters, pinholes and other defects are sometimes formed in the coating films aftera baking treatment for curing. It is more desirable that the content ofthe residual solvent or polymerization medium does not exceed 2% byweight.

The component (B) combined with the above described component (A) is acuring agent which is exemplified by polyisocyanate compounds or blockedisocyanate compounds such as isophorone diisocyanate, tolylenediisocyanate, xylylene diisocyanate, 4,4'-diphenyl methane diisocyanate,hexamethylene dissocyanate and the like, dimers and trimers thereof andpolyisocyanate compounds modified with a polyhydric alcohol, e.g.,trimethylol propane, and blocked at the isocyanate groups with ablocking agent such as ε-caprolactam, phenol, benzyl alcohol, methylethyl ketoxime and the like. The blocked isocyanate compound ispreferably solid at room temperature.

Further examples of the curing agent as the component (B) includedibasic aliphatic carboxylic acids, e.g., fumaric acid, succinic acid,adipic acid, azelaic acid, sebacic acid, dodecane dicarboxylic acid andthe like, acid anhydrides, e.g., phthalic anhydride, trimelliticanhydride, pyromellitic anhydride and the like, polyester resins oracrylic resins having an acid value of 10 to 300 mg KOH/g, glasstransition temperature of 30° to 120° C. and number-average molecularweight of 1000 to 15,000, dicyandiamide and derivatives thereof,imidazole and derivatives thereof, amine compounds such as diaminophenylmethane, cyclic amidine compounds and the like, melamine resins,glycidyl compound such ass diglycidyl terephthalate, diglycidylp-hydroxybenzoate, triglycidyl isocyanurate, spiroglycol diglycidylether, hidantoin compounds, alicyclic epoxy resins and the like,1,4-bis(2'-hydroxyethoxy) benzene, bis(hydroxyethyl) terephthalate,copolymers of styrene and allyl alcohol, spiroglycol,tris(2-hydroxyethyl) isocyanurate, hydroxy-containing polymericcompounds such as polyester resins and acrylic resins having a hydroxylvalue of 10 to 300 mg KOH/g, glass transition temperature of 30° to 120°C. and number-average molecular weight of 1000 to 15,000 and so on. Thecuring agent selected from the above named compounds is preferably solidat room temperature.

The thermosetting powdery coating composition of the present inventionis prepared by formulating the above described fluorine-containingcopolymer as the component (A) and the curing agent as the component (B)in a weight ratio in the range from 40:60 to 98:2 or, preferably, in therange from 50:50 to 97:3.

The thermosetting powdery coating composition of the present inventionhas a glass transition temperature in the range from 30° to 120° C. or,preferably, in the range from 35° to 100° C. When the glass transitiontemperature is too low, the composition is hardly in a condition ofsolid so that the composition cannot be used as a powdery coatingcomposition. When the glass transition temperature is too high, on otherhand, the powdery composition is poorly spreadable due to the increasein the softening point so that no uniform coating films can be obtained.

The thermosetting powdery coating composition of the invention shouldcontain volatile matters in an amount as small as possible. For example,the weight loss of the composition by heating should not exceed 5% byweight or, preferable, 2% by weight. When the weight loss by heating ofthe composition is too large, disadvantages are caused that the storagestability of the powdery coating composition is decreased and thecoating film formed from the coating composition is sometimes defectivedue to the formation of foams, blisters, pin holes and the like.

The thermosetting powdery coating composition of the present inventioncan be admixed according to need with various kinds of additivesconventionally formulated in coating compositions. Examples of theadditives compounded with the inventive powder coating compositioninclude pigments, i.e. inorganic pigments, e.g., titanium dioxide, redand yellow iron oxides, carbon black and the like, and organic pigments,e.g., phthalocyanine blue, phthalocyanine green, quinacridone-based redpigments, isoindolinone-based yellow pigment, and the like, extenderpigments such as talc, silica, calcium carbonate and the like, metalpowders such as aluminum powder, stainless steel powder and the like,mica flakes, levelling agents, ultraviolet absorbers, thermal agingretarders, foaming preventing agents and so on. These additives can beused wither singly or as a combination of two kinds or more according toneed. These additives can be compounded beforehand with either thecomponent (A) or the component (B).

The thermosetting powdery coating composition of the invention can beprepared by compounding the above described components in the samemanner as in the preparation of conventional thermosetting powderycoating compositions.

The thermosetting powdery coating composition prepared in the abovedescribed manner has a particle diameter not exceeding 40 μm and iscapable of forming a high-quality coating film on the surface ofsubstrates of metals and alloys such as iron, aluminum, copper, zinc,stainless steel, brass and the like in a uniform thickness by using anelectrostatic powder coating machine, fluidized immersion machine andthe like followed by baking in a hot air circulation oven, infraredoven, induction heating oven and the like.

In the following, the thermosetting powdery coating composition of theinvention is described in more detail by way of examples and comparativeexamples beginning with description for the preparation of thefluorine-containing copolymers. In the following description, the termsof "parts" and "%" all refer to "parts by weight" and "% by weight"respectively.

Preparation 1.

Into a stainless steel-made autoclave of 300 ml capacity equipped with astirrer were introduced 157 g of tert-butyl alcohol, 16 g of cyclohexylvinyl ether, 9 g of isobutyl vinyl ether, 25 g of hydroxybutyl vinylether, 1 g of potassium carbonate and 0.07 g of azobisisobutyronitrileto form a reaction mixture which was deaerated by repeating freezing andthawing using liquid nitrogen.

Then, 50 g of chlorotrifluoroethylene were introduced into the autoclaveand the temperature of the mixture was gradually increased up to 65° C.The reaction mixture was continuously agitated at the same temperaturefor 10 hours and the autoclave was cooled in water to terminate thereaction. After cooling to room temperature, the autoclave was releasedto discharge the unreacted monomers.

In the next place, the reaction mixture was heated at 60° C. under areduced pressure of 1 mmHg for 24 hours to remove the solvent. The thusobtained dry polymeric product was finely pulverized in a hammer mull togive a powdery fluorine-containing copolymer, which is referred to asthe copolymer A-1 hereinbelow.

The copolymer A-1 had a hydroxyl value of 120 mg KOH/g, glass transitiontemperature of 45° C. and intrinsic viscosity [η] of 0.21 as determinedat 30° C. in tetrahydrofuran. Analysis of the copolymer A1 indicatedthat the monomeric composition of the polymer was approximatelyidentical with that in the starting monomer mixture.

Preparation 2 to 5.

The procedure for the polymerization in each of these Preparations wassubstantially the same as in Preparation 1 described above except thatthe formulation of the starting monomer mixture was as indicated inTable 1 below and the amounts of tert-butyl alcohol as the solvent andazobisisobutyronitrile were adequately modified. The thus obtainedfluorine-containing copolymers are referred to as the copolymers A-2 toA-5 for the Preparations 2 to 5, respectively.

Table 1 below also shows the properties of the copolymers A-2 to A-5including the hydroxyl value, glass transition temperature, weight lossby heating, intrinsic viscosity and average molecular weight of thepolymeric molecular chains per one of the crosslinkable reactive groups.

Preparation 6.

The procedure for the polymerization of the monomer mixture wassubstantially the same as in the preceding Preparations except that theformulation of the starting monomer mixture was as indicated in Table 1below. Then, 100 parts of the thus obtained copolymer were dissolved in100 part s of xylene together with 0.9 part of succinic anhydride and0.05 part of triethyl benzyl ammonium chloride. The solution wasagitated at 100° C. for 3 hours in a flask followed by cooling.Thereafter, the solvent in the solution was removed by heating thesolution at 60° C. for 24 hours under a reduced pressure of 1 mmHg togive a dry polymeric product which was pulverized in a hammer mill intoa fine powder of the fluorine-containing copolymer. This powderyfluorine-containing copolymer, referred to as the copolymer A-6hereinbelow, had an acid value of 5 mg KOH/g indicating that carboxylgroups were introduced into the molecular structure of the copolymer.Table 1 below also shows the properties of this copolymer A-6.

                                      TABLE 1                                     __________________________________________________________________________    Copolymer No.    A-1  A-2  A-3  A-4  A-5  A-6                                 __________________________________________________________________________    Formulation of starting monomer mixture, g                                    CTFE             50   51   --   48   54   53                                  TFE              --   --   45   --   --   --                                  C-HXVE           16   28   45   32   23   17                                  EVE              --   10   --   --   13   10                                  IBVE              9   --   --   --   --    9                                  HBVE             25   11   10   20    5   11                                  VAC              --   --   --   --    5   --                                  Total            100  100  100  100  100  100                                 Properties of copolymer                                                       Hydroxyl value, mg KOH/g                                                                       120  55   50   94   26   46                                  Glass transition temperature, °C.                                                       45   48   35   50   35   45                                  Weight loss by heating, %                                                                      <2   <2   <2   <2   <2   <2                                  Intrinsic viscosity, dl/g                                                                         0.21                                                                               0.21                                                                               0.33                                                                               0.25                                                                               0.22                                                                               0.26                             Average molecular weight per one                                                               468  1020 1122 597  2158 1100                                crosslinkable reactive group                                                  __________________________________________________________________________     CTFE chlorotrifluoroethylene                                                  TFE tetrafluoroethylene                                                       CHXVE cyclohexyl vinyl ether                                                  EVE ethyl vinyl ether                                                         IBVE isobutyl vinyl ether                                                     HBVE hydroxybutyl vinyl ether                                                 VAC vinyl acetate                                                        

Preparation 7.

Into a stainless steel-made autoclave of 300 ml capacity equipped with astirrer were introduced 157 g of tert-butyl alcohol 18 g of cyclohexylvinyl ether, 10 g of isobutyl vinyl ether, 20 g of glycidyl vinyl ether,1 g of potassium carbonate and 0.07 g of azobisisobutyronitrile to forma reaction mixture which was deaerated by repeating freezing and thawingusing liquid nitrogen. Then, 52 g of chlorotrifluoroethylene wereintroduced into the autoclave and the temperature of the mixture wasgradually increased up to 65° C. The reaction mixture was continuouslyagitated for 10 hours at the same temperature to effect thepolymerization reaction and then the autoclave was cooled in water toterminate the polymerization reaction. After cooling to roomtemperature, the autoclave was released to discharge the unreactedmonomers. Thereafter, the solvent in the reaction mixture was removed byheating the mixture at 60° C. for 24 hours under a reduced pressure of 1mmHg to give a dry polymeric product which was then pulverized in ahammer mill to give a fine powdery of the fluorine-containing copolymer.

The thus obtained fine powder of the fluorine-containing copolymer,referred to as the copolymer A-7 hereinbelow, had an epoxy equivalent of500 g/eq., glass transition temperature of 49° C. and intrinsicviscosity of 0.19 as determined at 30° C. in tetrahydrofuran. Analysisof the copolymer A-7 indicated that the monomeric composition of thecopolymer was approximately identical with that in the starting monomermixture.

Preparations 8 to 10.

The procedure for the polymerization reaction was substantially the sameas in the preceding example except that the formulation of the startingmonomer mixture in each of these examples was as indicated in Table 2below and the amounts of tert-butyl alcohol as the solvent andazobisisobutyronitrile as the polymerization initiator were adequatelymodified.

Table 2 also shows the properties of the thus obtainedfluorine-containing copolymers in Examples 8 to 10, referred to as thecopolymers A-8 to A-10, respectively, including the epoxy equivalent,glass transition temperature, weight loss by heating and intrinsicviscosity as determined at 30° C. in tetrahydrofuran. The weight loss byheating was determined according to the method specified in JIS K 5400,8.3.

                  TABLE 2                                                         ______________________________________                                        Copolymer No.                                                                             A-7      A-8      A-9    A-10                                     ______________________________________                                        Formulation of starting monomer mixture, g                                    CTFE        52       55       48     30                                       TFE         --       --       --     21                                       C-HXVE      18       35       32     20                                       EVE         --       --       15     --                                       IBVE        10       --       --     14                                       VAC         --       --       --     13                                       GVE         20       10       --      2                                       AGE         --       --        5     --                                       Total       100      100      100    100                                      Properties of copolymer                                                       Epoxy equivalent,                                                                         500      997      2180   10861                                    g/eq.                                                                         Glass transition                                                                          49       55       51     37                                       temperature, °C.                                                       Weight loss by                                                                            <2       <2       <2     <2                                       heating, %                                                                    Intrinsic viscosity,                                                                         0.19     0.20     0.15                                                                                 0.24                                  dl/g                                                                          ______________________________________                                         GVE glycidyl vinyl ether                                                      AGE allyl glycidyl ether                                                      See footnote to Table 1 for CTFE, TFE, CHXVE, EVE, IBVE and VAC.         

Preparation 11.

A fluorine-containing copolymer was prepared in substantially the samemanner as in Preparation 7 except that the starting monomer mixture wascomposed of 52 g of chlorotrifluoroethylene, 28 g of cyclohexyl vinylether and 20 g of hydroxybutyl vinyl ether. Then, 100 parts of thecopolymer was dissolved in 100 parts of xylene together with 3.6 partsof succinic anhydride and 0.05 part of triethyl benzyl ammonium chlorideand the solution was continuously agitated for 3 hours at 100° C. in aflask followed by cooling. Thereafter, the solvent in the solution wasremoved by heating the solution at 60° C. for 24 hours under a reducedpressure of 1 mmHg to give a dry polymeric product which was pulverizedin a hammer mill into a fine powder of the fluorine-containingcopolymer, referred to as the copolymer A-11 hereinbelow.

Table 3 below shows the properties of the copolymer A-11 including theacid value, glass transition temperature, weight loss by heating,intrinsic viscosity as determined at 30° C. in tetrahydrofuran andaverage molecular weight of the polymeric molecules per one of thecrosslinkable reactive groups.

Preparations 12 to 14.

The procedure was substantially the same as in the preceding preparationexcept that the formulation of the starting monomer mixture and theamount of succinic anhydride for the modification of the copolymers wereas indicated in Table 3 and the amounts of tert-butyl alcohol andazobisisobutyronitrile were adequately modified to give powderyfluorine-containing copolymers referred to as the copolymers A-12 toA-14 hereinbelow. Table 3 below shows the properties of thesecopolymers.

                  TABLE 3                                                         ______________________________________                                        Copolymer No.                                                                              A-11     A-12     A-13   A-14                                    ______________________________________                                        Formulation of starting monomer mixture, g                                    CTFE         52       55       48     51                                      C-HXVE       28       15       --     --                                      EVE          --       10       --     10                                      HBVE         20       --       15     25                                      IBVE         --        5       12     14                                      IPVE         --       10       15     --                                      VAC          --        5       10     --                                      Total        100      100      100    100                                     Succinic anhydride for                                                                       3.6      1.8      0.9    5.0                                   modification, g                                                               Properties of copolymer                                                       Acid value, mg                                                                               19.5   10        5       26.7                                  KOH/g                                                                         Glass transition                                                                           47       42       36     37                                      temperature, °C.                                                       Weight loss by                                                                             <2       <2       <2     <2                                      heating, %                                                                    Intrinsic viscosity,                                                                          0.21     0.16     0.23                                                                                 0.24                                 dl/g                                                                          Average molecular                                                                          2877     5610     11220  2101                                    weight per one                                                                crosslinkable                                                                 reactive group                                                                ______________________________________                                         IPVE isopropyl vinyl ether                                                    See footnote to Table 1 for CTFE, CHXVE, EVE, IBVE and VAC.              

EXAMPLES 1 TO 8 AND COMPARATIVE EXAMPLES 1 TO 4.

Thermosetting powdery coating composition were prepared in theseExamples and Comparative Examples each by uniformly compounding eitherone of the copolymers A-1 to A-6 (Examples) or a commercial product of apolyester or acrylic resin (Comparative Examples) shown in Table 4 belowas the component (A) in an amount shown in Table 4, a curing agent asthe component (B) of the kind and in an amount shown in Table 4, 30parts of titanium dioxide and 0.5 part of a levelling agent (Modaflow, aproduct by Monsanto Co.).

The resinous ingredients used as the component (A) in the ComparativeExamples were as shown below.

a-1: polyester containing no solvent and having an acid value of 30 mgKOH/g (Ester Resin ER-6610, a product by Nippon Ester Co.)

a-2: polyester resin containing no solvent and having an acid value of30 mg KOH/g (Finedick M-8020, a product by Dai-Nippon Ink Chemical Co.)

a-3: acrylic resin containing no solvent and having an epoxy equivalentof 630 g/eq. (Finedick A-223S, a product by Dai-Nippon Ink Chemical Co.)

a-4: acrylic resin containing no solvent and having an epoxy equivalentof 455 g/eq. (Almatex PD-7210, a product by Mitsui Toatsu Chemical Co.)

Further, the curing agents used as the component (B) in the Examples andComparative Examples were as follows.

B-1: ε-caprolactam blocked isocyanate containing no solvent (AdductB-1530, a product by Huls Co.)

B-2: urethodione compound containing no solvent (Adduct BF-1540, aproduct by Huls Co.)

B-3: pyromellitic anhydride

B-4: dodecane dicarboxylic acid

Table 4 below gives the kinds and amounts of the component (A), i.e. A-1to A-6 or a-1 to a-4, and the component (B), i.e. B-1 to B-4, weightratio of the component (B) to the component (A) and the weight loss byheating of the blend of the components (A) and (B) determined accordingto the method specified in JIS K 5400, 8.3.

The blend of the components (A) and (B), titanium dioxide and levellingagent was uniformly mixed for about 1 minute in a dry blender (HenschelMixer, manufactured by Mitsui Kakoki Co.) and then kneaded under moltencondition at 80° C. to 100° C. in an extrusion kneader (Buss Ko KneaderPR-46, manufactured by Buss Co.). The resin blend discharged out of thekneader was cooled and finely pulverized in a hammer mill into a finepowder from which coarser particles were removed by passing through ascreen of 150 mesh fineness to give a thermosetting powdery coatingcomposition. A steel test panel having a thickness of 0.8 mm after azinc phosphate treatment was coated with the powdery coating compositionby the method of electrostatic coating followed by a baking treatmentfor 20 minutes at a baking temperature indicated in Table 5 below togive a cured coating film having a thickness of 40 μm.

The test panels coated in the above described manner were subjected tothe tests of several items for the coating films according to thetesting procedure and giving the results shown below and in Table 5.

                  TABLE 4                                                         ______________________________________                                        Component  Component                                                          (A)        (B)       Weight ratio of                                                                           Weight loss by                               (parts)    (parts)   (B):(A)     heating, %                                   ______________________________________                                        Example                                                                       1    A-1 (43.5)                                                                              B-1 (26.0)                                                                              37:63     1.8                                        2    A-2 (54.5)                                                                              B-1 (15.0)                                                                              22:78     1.9                                        3    A-3 (55.6)                                                                              B-1 (13.9)                                                                              20:80     1.7                                        4    A-4 (47.3)                                                                              B-1 (22.2)                                                                              32:68     1.3                                        5    A-5 (61.5)                                                                              B-1 (8.0) 12:88     1.2                                        6    A-6 (56.5)                                                                              B-1 (13.0)                                                                              19:81     1.1                                        7    A-6 (56.5)                                                                              B-2 (13.0)                                                                              19:81     1.0                                        8    A-6 (65.2)                                                                              B-3 (4.3)  6:94     1.2                                        Comparative Example                                                           1    a-1 (60.5)                                                                              B-1 (9.0) 13:87     1.3                                        2    a-2 (60.5)                                                                              B-1 (9.0) 13:87     1.9                                        3    a-3 (59.7)                                                                              B-4 (9.8) 14:86     1.6                                        4    a-4 (56.6)                                                                              B-4 (12.9)                                                                              19:81     1.8                                        ______________________________________                                    

1) Apparatus of the coating film relative to the smoothness andreflectiveness by visual inspection of the reflected image of afluorescent lamp which may be with or without deformation: good in eachof Examples 1 to 8 and Comparative Example 1 to 4

2) Surface luster (60° mirror surface luster) according to JIS K 5400,6.7: results given in Table 5 in %

3) Impact resistance according to JIS K 5400, 6.13 B impact deformationtest using a DuPont type impact tester with 1/2 inch diameter, 1 kg loadand 50 cm height: good in each of Examples 1 to 8 and ComparativeExamples 1 and 2 without breaking or exfoliation of the coating film butno good in Comparative Example 3 and 4 with breaking and exfoliation ofthe coating film

4) Flexibility by Erichsen tester according to JIS B 7777: 7 mm in eachof Examples 1 to 8 and Comparative Example 1 to 4

5) Adhesion of coating film by checkerboard testing method according toJIS D 0202, 8.12 forming 100 checkerboard squares of 1 mm×1 mm,cellophane-based pressure-sensitive adhesive tape of 12 mm width appliedand bonded to the surface and then rapidly pulled apart by holding thetape end perpendicularly to the surface: 100/100 in each of Examples 1to 8 and Comparative Examples 1 to 4

6) Insusceptibility to stain, line marking with a felt pen ofsolvent-type black ink and wiping off after 24 hours at 20° C. with agauze wet with xylene to examine the condition of line trace: absolutelyno line trace in each of Examples 1 to 8, faint but noticeable linetrace in Comparative Examples 3 and 4 and clearly noticeable line tracein Comparative Examples 1 and 2

7) Weatherability by accelerated weathering test according to JIS D0205, 7.6 for luster retention and color difference ΔE after 1000 hoursand 3000 hours using Sunshine Carbon Weathermeter

                                      TABLE 5                                     __________________________________________________________________________                     Weatherability                                                      Baking    After 1000 hours                                                                           After 3000 hours                                       temper-                                                                            Surface                                                                            Luster re-                                                                          Color dif-                                                                           Luster re-                                                                          Color dif-                                       ature, °C.                                                                  luster                                                                             tention, %                                                                          ference, ΔE                                                                    tention, %                                                                          ference, ΔE                         __________________________________________________________________________    Example                                                                       1      190  85   99    0.6    97    1.0                                       2      190  84   98    0.7    96    1.3                                       3      190  86   99    0.3    97    0.9                                       4      190  85   97    0.4    95    0.8                                       5      190  83   98    0.5    94    1.1                                       6      190  84   99    0.5    96    1.2                                       7      190  89   98    0.6    96    0.8                                       8      210  87   99    0.2    98    0.5                                       Comparative                                                                   Example                                                                       1      190  87   20    1.5    10    3.5                                       2      190  88   23    1.7    15    3.2                                       3      190  89   68    1.3    30    3.1                                       4      180  90   64    1.3    27    2.9                                       __________________________________________________________________________

EXAMPLES 9 TO 20 AND COMPARATIVE EXAMPLES 5 TO 10.

Thermosetting powdery coating compositions were prepared in theseExamples and Comparative Examples each by uniformly compounding eitherone of the copolymers A-7 to A-14 (Examples) or one of the commercialresin products a-1 to a-6 shown below (Comparative Examples) as thecomponent (A) in an amount indicated in Table 6 below, one of the curingagents B-1, B-4 and B-6 to B-10 shown below as the component (B) in anamount indicated in Table 6, 30 parts of titanium dioxide in each of theformulations other than Example 9 and Comparative Examples 5 and 10, 0.5part of a levelling agent (Modaflow, supra) in each of the formulationsother than Comparative Example 5 and 0.5 part of benzoin in each of theformulations other than Comparative Example 5.

The resinous ingredients used in Comparative Examples as the component(A) were as follows.

a-1 to a-4: see preceding Comparative Examples.

a-5: fluorocarbon resin containing no solvent (Fostaflon, a product byHechst Co.)

a-6: polyester resin containing no solvent and having an acid value of30 mg KOH/g (Uralac P-2400, a product by DSM Co.)

Further, the curing agents used as the component (B) in the Examples andComparative Examples were as follows.

B-1 and B-4: see the preceding Examples.

B-5: trimellitic anhydride

B-6: polyester resin containing no solvent and having an acid value of220 mg KOH/g (Finedic M-8540, a product by Dai-Nippon Ink Chemical Co.)

B-7: dicyandiamide

B-8: adipic acid dihydrazide

B-9: diglycidyl terephthalate

B-10: triglycidyl isocyanurate

Each of the blends in Examples 9 to 20 and Comparative Examples 5 to 10was processed into a thermosetting powdery coating composition in justthe same manner as in the preceding Examples and the coatingcompositions were subjected to the evaluation tests in the same manneras in the preceding Examples to give the results shown below and inTable 7. The baking treatment of the coating film was performed for 20minutes at a temperature indicated in Table 7 and the coating film had athickness of 40 μm. The appearance of the coating films was good in eachof the Examples and Comparative Examples with complete smoothnessexcepting Comparative Example 5 in which the appearance of the coatingfilm was poor. The impact resistance of the coating films was good ineach of the Examples and Comparative Examples 5 to 7 but poor inComparative Examples 8 to 10. The flexibility of the coating films was 7mm in each of the Examples and Comparative Examples. The adhesion of thecoating films to the substrate surface by the checkerboard test was100/100 in each of the Examples and Comparative Examples exceptingComparative Example 5 in which the result was 0/100. Theinsusceptibility to stain of the coating films was good in each of theExamples with absolutely no line traces while faint but noticeable linetrace was found in Comparative Examples 5, 9 and 10 and clearlynoticeable line trace was found in Comparative Examples 6 to 8.

                  TABLE 6                                                         ______________________________________                                        Component  Component                                                          (A)        (B)       Weight ratio of                                                                           Weight loss by                               (parts)    (parts)   (B):(A)     heating, %                                   ______________________________________                                        Example                                                                        9   A-7 (80.3)                                                                              B-4 (18.7)                                                                              19:81     1.3                                        10   A-7 (56.0)                                                                              B-4 (13.0)                                                                              19:81     1.2                                        11   A-7 (66.2)                                                                              B-7 (2.8) 4:96      1.1                                        12   A-7 (63.5)                                                                              B-8 (5.5) 8:92      1.4                                        13   A-7 (45.7)                                                                              B-6 (23.3)                                                                              34:66     1.6                                        14   A-8 (64.8)                                                                              B-5 (4.2) 6:94      1.7                                        15   A-9 (61.5)                                                                              B-6 (7.5) 11:89     1.3                                        16   A-10 (66.9)                                                                             B-4 (2.1) 4:96      1.9                                        17   A-11 (66.1)                                                                             B-10 (2.9)                                                                              4:96      1.2                                        18   A-12 (66.5)                                                                             B-9 (2.5) 4:96      1.1                                        19   A-13 (66.9)                                                                             B-9 (2.1) 3:97      1.9                                        20   A-14 (65.1)                                                                             B-10 (3.9)                                                                              6:94      1.5                                        Comparative Example                                                            5   a-5 (100)  --        0:100    1.6                                         6   a-1 (60.0)                                                                              B-1 (9.0) 13:87     1.7                                         7   a-2 (60.0)                                                                              B-1 (9.0) 13:87     1.3                                         8   a-6 (64.2)                                                                              B-10 (4.8)                                                                              7:93      1.9                                         9   a-3 (59.2)                                                                              B-4 (9.8) 14:86     1.8                                        10   a-4 (56.1)                                                                              B-4 (12.9)                                                                              19:81     1.4                                        ______________________________________                                    

The results of the weatherability test were given in three ratings of Afor at least 85% of luster retention and a color difference smaller than1.5, B for 60 to 85% luster retention and a color difference smallerthan 3.0 and C for luster retention smaller than 60% and/or colordifference of 3.0 or larger.

                  TABLE 7                                                         ______________________________________                                               Baking           Weatherability                                               temper-                                                                              Surface   After     After                                              ature, °C.                                                                    luster    1000 hours                                                                              3000 hours                                  ______________________________________                                        Example                                                                        9       180      89        A       A                                         10       180      88        A       A                                         11       180      87        A       A                                         12       170      89        A       A                                         13       200      90        A       A                                         14       180      86        A       A                                         15       200      89        A       A                                         16       180      88        A       A                                         17       180      90        A       A                                         18       190      87        A       A                                         19       190      86        A       A                                         20       180      88        A       A                                         Comparative                                                                   Example                                                                        5       380      27        A       A                                          6       190      87        C       C                                          7       190      88        C       C                                          8       190      90        B       C                                          9       190      89        B       C                                         10       180      87        B       C                                         ______________________________________                                    

As is clear from the results obtained in Examples 1 to 20, the coatingfilms obtained from the inventive thermosetting powdery coatingcompositions are excellent in respect of the appearance, surface luster,impact resistance, flexibility, adhesion to the substrate surface,insusceptibility to stain and weatherability.

In contrast thereto, the coating films in Comparative Examples 1 to 2obtained from a conventional polyester resin-based powdery coatingcomposition are inferior in respect of the insusceptibility to stain andweatherability and the coating films in Comparative Examples 3 and 4obtained from a conventional acrylic resin based coating composition areinferior in respect of the impact resistance, insusceptibility to stainand weatherability.

The thermoplastic powdery coating composition based on a fluorocarbonresin in Comparative Example 5 requires an extremely high bakingtemperature and the coating film prepared therefrom is inferior inrespect of the appearance, surface luster, adhesion to the substratesurface and insusceptibility to stain. The coating films in ComparativeExamples 6 to 8 obtained from a conventional polyester resin-basedpowdery coating composition are inferior in respect of theinsusceptibility to stain and weatherability. The coating films inComparative Examples 9 and 10 obtained from a conventional acrylicresin-based coating composition are inferior in respect of the impactresistance, insusceptibility to stain and weatherability.

To summarize, the thermosetting powdery coating composition of thepresent invention is very superior in respect of the workability in thecoating works and the dispersibility of pigments as compared withthermoplastic fluorocarbon resin-based powdery coating compositions andthe coating films obtained therefrom are excellent in respect of theadhesion to the substrate surface, surface luster, insusceptibility tostain, impact resistance and flexibility and also have much higherweatherability than any of conventional thermosetting powdery coatingcompositions. Accordingly, the inventive coating composition is veryuseful in all fields of applications in which a powdery coatingcomposition is required. When comparison is made with conventionalsolution-type fluorocarbon resin-based coating compositions, moreover,the inventive coating composition is advantageous in respect of savingof materials and absence of the problems of environmental pollution aswell as in respect of easiness in the process control and processautomatization consequently with a great improvement in the efficiencyof the coating works.

For example, a single coating with the inventive coating composition maygive a coating film having a large thickness as desired so that theproductivity of the coating works can be greatly improved to provide acoating film having full durability.

What is claimed is:
 1. A thermosetting powdery coating composition whichcomprises, in admixture:(A) from 40 to 98 parts by weight of afluorine-containing copolymer comprising a monomeric moiety derived froma fluoroolefin compound and having hydroxyl groups as the crosslinkablereactive groups of which the content of fluorine is at least 10% byweight, the intrinsic viscosity determined at 30° C. in tetrahydrofuranis in the range from 0.05 to 2 dl/g, the glass transition temperature isin the range from 35° C. to 120° C. and the weight loss by heating doesnot exceed 2%; and (B) from 60 to 2 parts by weight of a blockedisocyanate compound as the curing agent capable of forming crosslinks byreacting with the crosslinkable reactive groups in thefluorine-containing copolymer.
 2. The thermosetting powdery coatingcomposition of claim 1 wherein the fluoroolefin compound is selectedfrom the group consisting of tetrafluoroethylene,chlorotrifluoroethylene, trifluoroethylene, vinylidene, fluoride,hexafluoropropylene and pentafluoropropylene.
 3. The thermosettingpowdery coating composition of claim 1 wherein the content of fluorinein the fluorine-containing copolymer is in the range from 15 to 72% byweight.
 4. The thermosetting powdery coating composition of claim 1wherein the fluorine-containing copolymer is a copolymer of a monomericmixture comprising a fluoroolefin compound and a comonomercopolymerizable therewith and having a crosslinkable reactive group. 5.The thermosetting powdery coating composition of claim 4 wherein themonomeric mixture contains from 30 to 70% by moles of the fluoroolefincompound.
 6. The thermosetting powdery coating composition of claim 1wherein the fluorine-containing copolymer has a hydroxyl value in therange from 1 to 200 mg KOH/g.
 7. The thermosetting powdery coating ofclaim 1 wherein the fluorine-containing copolymer has a hydroxyl valuein the range from 20 to 140 mg KOH/g.
 8. The thermosetting powderycoating composition of claim 7 wherein the glass transition temperatureis in the range from 45° to 120° C.
 9. The thermosetting powdery coatingcomposition as claimed in claim 8, wherein the fluorine-containingcopolymer is a copolymer of a monomeric mixture comprising afluoroolefin compound and a comonomer copolymerizable therewith andhaving a crosslinkable reactive group.
 10. The thermosetting powderycoating composition as claimed in claim 9 wherein the monomeric mixturecontains from 30 to 70% by moles of the fluoroolefin compound.
 11. Thethermosetting powdery coating composition of claim 1 wherein the glasstransition temperature is in the range from 45° to 120° C.
 12. Thethermosetting powdery coating composition as claimed in claim 9 wherein(A) and (B) are in a weight ratio of 50:50 to 97:3.
 13. Thethermosetting powdery coating composition as claimed in claim 12,wherein the glass transition temperature is 35° to 100° C.
 14. Thethermosetting powdery coating composition as claimed in claim 13,wherein the composition has a particle diameter not exceeding 400 μm.